The present invention relates to a new and improved construction of opening roll for an open-end spinning device for opening a fiber sliver with the aid of needles which are inserted by means of their needle shafts into bores provided in a cylindrical body, wherein the points of the needles protrude from such cylindrical body.
In prior art opening rolls of the above-mentioned type, for instance as disclosed in the German Patent Publication No. 2,529,336 and the corresponding U.S. Pat. No. 4,058,965, granted Nov. 22, 1977, it is difficult, during mounting of the needles in the very narrow bores receiving the needle base, to attain an exact central, i.e., coaxial position of each needle in its related narrow bore. Due to for instance imprecise insertion, needle bending during insertion or imprecise needle profiles or cross-sectional shapes, an annular gap is formed between the needle and the wall of the bore. This annular gap tapers off along the needle and, viewed in cross-section, is of essentially crescent configuration. In these gaps there are entrapped fibers. This results in undesirable fiber accumulations on the needles and thus on the roll surface. When this happens there is not only impaired the opening performance of the needles, that is to say their efficiency, due to increasing blockage by the accumulated fiber material, but there also result uncontrolled breaking loose of such fiber accumulations which causes uncontrolled and disorderly fiber feed to the fiber collecting surface of the open-end spinning device. This in turn produces an uneven yarn due to the disturbed fiber supply. If the transition point between the cylindrical needle shaft and the conical, pointed needle section is located below the roll surface, i.e., if the conical needle section also extends within the needle shaft bore, then there are intensified the aforementioned disturbances because already by virtue of the conicity of the needle there is formed a tapered, annular gap along the needle.